Cargo package manager

Cargo is a tool that allows Rust projects to declare their various dependencies and ensure that you’ll always get a repeatable build.
To accomplish this goal, Cargo does four things:
* Introduces two metadata files with various bits of project information.
* Fetches and builds your project’s dependencies.
* Invokes rustc or another build tool with the correct parameters to build your project.
* Introduces conventions to make working with Rust projects easier.